No. There were prisons also.
Gulag managed "correctional camps". It is acronym for "главное [main]; управление [administration]; лагерей [of the camps]".
As far as I know initially "correctional camps" were "light" versions of prisons. Prisoners in camps have more personal freedom in comparison to prisoners who were locked in prison's cells.
However, with Gulag system, forced labor was introduced. Also "special correctional camps" were introduced for "very dangerous criminals". They were located in the places with extreme conditions. Far north, uranium mines and so on.